Fluorinated ion exchange polymers having carboxylic acid and/or sulfonic acid functional groups or salts thereof are known in the art. One principal use of such polymers is as a component of a membrane used to separate the anode and cathode compartments of a chloralkali electrolysis cell. Such membrane can be in the form of a reinforced or unreinforced film or laminar structure.
Use of reinforcement within a membrane, while making it stronger, is not totally beneficial. One deleterious effect is that use of reinforcement such as fabric results in a thicker membrane, which in turn leads to operation at higher voltage because the greater thickness results in a higher electrical resistance. Additionally, thick layers of polymer at the junctions of threads in a reinforcing fabric also constitute regions of high resistance. (By "junctions" is meant the crossover points where threads in the warp meet threads in the weft.) A second deleterious effect, which also leads to operation at higher voltage, is caused by a "shadowing" effect of the reinforcing members. The shortest path for an ion through a membrane is a straight perpendicular path from one surface to the other surface. Reinforcement members are uniformly fabricated of substance which is not ion-permeable. Those parts of a membrane where an ion cannot travel perpendicularly straight through the membrane, and from which the ion must take a circuitous path around a reinforcng member, are termed "shadowed areas". Introduction of shadowed areas into a membrane by use of reinforcement in effect leads to a reduction in the portion of the membrane which actively transports ions, and thus increases the operating voltage of the membrane.
It is thus desirable to provide, for use in a chloralkali cell, unreinforced membrane capable of operation at low voltage and high current efficiency, and thereby at low power consumption, so as to provide products of high purity at low cost, especially in view of today's high cost of energy.
In view of the current trend in the chloralkali industry toward use of zero gap and narrow gap cells, so as to minimize the contribution of electrolyte resistance to total cell voltage, it is also important to provide for use in such cells unreinforced membrane which is capable of operating at low voltage and high current efficiency.
It is a principal object of this invention to provide unreinforced ion exchange membrane which operates at low voltage and high current efficiency, and thereby at low power consumption.
It is a specific object of this invention to provide unreinforced membrane especially adapted for use in zero-gap and narrow-gap chloralkali cells. Other objects will be apparent hereinbelow.